User:Jtwsaddress42/Projects/Project 2/Sections/Chapter 13/Identity & Innate Immunity

Metchnikoff's accidental discovery of the white blood cell, or lymphocyte, in a star fish that he had skewered with a thorn inspired his research into phagocytosis; and, lead him to the concept of a system of innate host immunity in animals where the white blood cells, phagocytes, patrol the body looking for foreign invaders and damaged cells to consume. He reasoned that they were a cell lineage that had retained their ancestral role of distinguishing self from non-self in early animal colonies - and, therefore represented a primitive state for that cellular population in animals.

This population of cells was not only responsible for ejecting foreign invaders but was also responsible for dealing with sick and damaged cells of the body - as well as those emitting apoptotic signals. In addition to facilitating the process of defense, these cells participate in the processes of metamorphosis.